Solid fuel gasification under a pressure of 10 to 150 bars by a treatment with oxygen and with steam and/or carbon dioxide as gasifying agents, is known. In such processes the fuel in the reactor constitutes a fixed bed, which slowly subsides, the gasifying agents are introduced into said bed through a rotating grate, which rotates at a controlled speed, and the incombustible mineral constituents are withdrawn as ash by the action of the rotating grate and are delivered to a lock chamber container, which is periodically closed, pressure-relieved and emptied.
The gasification of granular coal in a fixed bed is known and has been described, e.g. in Ullmanns Enzyklopadie der technischen Chemie, 4th edition (1977), Volume 14, pages 383 to 386. Details of the design of the reactor and of the associated rotating grate are apparent from German Pat. Nos. 23 51 963; 23 46 833; 25 24 445; and open German application DE-OS No. 26 07 964; and the corresponding U.S. Pat. Nos. 3,930,811; 3,937,620; 4,014,664; 4,088,455.
The gasification reactor is generally supplied with granular coal having particle sizes from about 3 to 70 mm; a certain proportion of fine-grained coal is permissible. In addition to coal, brown coal or lignite and peat can be gasified in a fixed bed.
In the operation of known gasification reactors, it was customary to control mainly the supply of the gasifying agents and this control was preferably performed manually by operators. The control was preferably performed in dependence on the exit temperature of the product gas.
When channeling occasionally occurred during the gasification, i.e. when the gasifying agents were flowing upwardly in the fixed bed through channels formed at random in the fixed bed so that the gasifying agents had only a little effect, the exit temperatures of the product gas increased.
That disturbance was counteracted by a change of the speed of the rotating grate.
It has since been found that the grate speed is of great significance for the operation of the gasification reactor and must be very sensitively adjusted. If the speed of the grate is repeatedly changed in a short time, the gasification operation may become unbalanced and particularly the height of the ash layer over the rotating grate may vary greatly. If the ash bed is too low and, as a result, the ash temperature is too high, the material of the rotating grate will be endangered and cracks may form in the parts of the grate.